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dnsmasq/src/config.h
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Simon Kelley 014e909f78 Rework storage allocation for domain names. CVE-2026-2291 
This is the stable release fix for CVE-2026-2291

Dnsmasq recieves and sends domain names within DNS packets in RFC-1035
format, a string of counted labels terminated by a zero length label.
Internally to dnsmasq, domain names are represented as zero-terminated C strings
with the labels seperated by '.' characters, like the normal presentation
format for domain names.

The RFC-1035 limit for a domain name in wire format is 255 octets, and
when converted to presentation format, this makes a string of
maximum 253 characters. However dnsmasq needs to be able to
represent any 8-bit character within a label, and this causes
problems with /000 (which would terminate the c-string early) and
'.' (which would terminate a label early). To avoid this, dnsmasq
escapes both of these characters, which means that they take two bytes
in the string. The domain name with must charaters in it has four labels
and the 255 octet wire length limits these four labels to a total of
250 characters. The other five octets are the four label length bytes
and the zero length byte terminator. If all 250 characters need escaping
that makes the maximum length of the dnsmasq internal format 503
characters (250 escaped characters in labels, amd three dots between
four labels) Since this format is zero-terminated c-string, buffers
have to be allocated as 504 bytes.

This arrangement grew in a somewhat ad-hoc manner and early dnsmasq
didn't do the escaping trick, and didn't really differentiate between
the lengths of the wire format and the presentation format, since
they were very similar. It also, for reasons lost in time, inherited
a defintion for MAXDNAME from early BIND headers, set at 1025 bytes.
This value was used as the buffer size for both wire and presentation
formats.

This patch makes everything consistent. It declares two constants

MAXDNAME 255     /* max size of wire format domain name */
MAXDNAMESTR 503  /* max size of internal format created from a 255 octet wire format name */

All internal name buffers are allocated as MAXDNAMESTR+1 bytes,
to hold a maximum size internal format name and zero termination.

Names parsed out of incoming packets are rejected if their
wire format is greater than 255 bytes, which ensures that
their internal representation cannot exceed 503 characters.
Names inserted into outgoing packets are failed similarly if
they exceed 255 bytes. (this would in theory be possible
for a legal internal-representaion name if it has at least
one unescaped character in a label.
2026-05-10 21:49:39 +01:00

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/* dnsmasq is Copyright (c) 2000-2026 Simon Kelley
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 dated June, 1991, or
(at your option) version 3 dated 29 June, 2007.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#define FTABSIZ 150 /* max number of outstanding requests (default) */
#define MAX_PROCS 30 /* default max no children for TCP requests */
#define CHILD_LIFETIME 150 /* secs 'till terminated (RFC1035 suggests > 120s) */
#define TCP_MAX_QUERIES 100 /* Maximum number of queries per incoming TCP connection */
#define TCP_TIMEOUT 5 /* timeout waiting to connect to an upstream server - double this for answer */
#define TCP_BACKLOG 32 /* kernel backlog limit for TCP connections */
#define EDNS_PKTSZ 1232 /* default max EDNS.0 UDP packet from from /dnsflagday.net/2020 */
#define KEYBLOCK_LEN 40 /* choose to minimise fragmentation when storing DNSSEC keys */
#define NAMEBLOCK_CHARS 1500 /* quantum of memory allocation for names from /etc/hosts */
#define DNSSEC_LIMIT_WORK 40 /* Max number of queries to validate one question */
#define DNSSEC_LIMIT_SIG_FAIL 20 /* Number of signature that can fail to validate in one answer */
#define DNSSEC_LIMIT_CRYPTO 200 /* max no. of crypto operations to validate one query. */
#define DNSSEC_LIMIT_NSEC3_ITERS 150 /* Max. number if iterations allowed in NSEC3 record. */
#define DNSSEC_ASSUMED_DS_TTL 3600 /* TTL for negative DS records implied by server=/domain/ */
#define TIMEOUT 10 /* drop UDP queries after TIMEOUT seconds */
#define SMALL_PORT_RANGE 30 /* If DNS port range is smaller than this, use different allocation. */
#define FORWARD_TEST 50 /* try all servers every 50 queries */
#define FORWARD_TIME 20 /* or 20 seconds */
#define UDP_TEST_TIME 60 /* How often to reset our idea of max packet size. */
#define SERVERS_LOGGED 30 /* Only log this many servers when logging state */
#define LOCALS_LOGGED 8 /* Only log this many local addresses when logging state */
#define LEASE_RETRY 60 /* on error, retry writing leasefile after LEASE_RETRY seconds */
#define CACHESIZ 150 /* default cache size */
#define TTL_FLOOR_LIMIT 3600 /* don't allow --min-cache-ttl to raise TTL above this under any circumstances */
#define MAXLEASES 1000 /* maximum number of DHCP leases */
#define PING_WAIT 3 /* wait for ping address-in-use test */
#define PING_CACHE_TIME 30 /* Ping test assumed to be valid this long. */
#define DECLINE_BACKOFF 600 /* disable DECLINEd static addresses for this long */
#define DHCP_PACKET_MAX 16384 /* hard limit on DHCP packet size */
#define SMALLDNAME 75 /* most domain names are smaller than this */
#define CNAME_CHAIN 10 /* chains longer than this atr dropped for loop protection */
#define DNSSEC_MIN_TTL 60 /* DNSKEY and DS records in cache last at least this long */
#define HOSTSFILE "/etc/hosts"
#define ETHERSFILE "/etc/ethers"
#define DEFLEASE 3600 /* default DHCPv4 lease time, one hour */
#define DEFLEASE6 (3600*24) /* default lease time for DHCPv6. One day. */
#define CHUSER "nobody"
#define CHGRP "dip"
#define TFTP_MAX_CONNECTIONS 50 /* max simultaneous connections */
#define TFTP_MAX_WINDOW 32 /* max window size to negotiate */
#define TFTP_TRANSFER_TIME 120 /* Abandon TFTP transfers after this long. Two mins. */
#define LOG_MAX 5 /* log-queue length */
#define RANDFILE "/dev/urandom"
#define DNSMASQ_SERVICE "uk.org.thekelleys.dnsmasq" /* Default - may be overridden by config */
#define DNSMASQ_PATH "/uk/org/thekelleys/dnsmasq"
#define DNSMASQ_UBUS_NAME "dnsmasq" /* Default - may be overridden by config */
#define AUTH_TTL 600 /* default TTL for auth DNS */
#define SOA_REFRESH 1200 /* SOA refresh default */
#define SOA_RETRY 180 /* SOA retry default */
#define SOA_EXPIRY 1209600 /* SOA expiry default */
#define LOOP_TEST_DOMAIN "test" /* domain for loop testing, "test" is reserved by RFC 2606 and won't therefore clash */
#define LOOP_TEST_TYPE T_TXT
#define DEFAULT_FAST_RETRY 1000 /* ms, default delay before fast retry */
#define STALE_CACHE_EXPIRY 86400 /* 1 day in secs, default maximum expiry time for stale cache data */
/* compile-time options: uncomment below to enable or do eg.
make COPTS=-DHAVE_BROKEN_RTC
HAVE_BROKEN_RTC
define this on embedded systems which don't have an RTC
which keeps time over reboots. Causes dnsmasq to use uptime
for timing, and keep lease lengths rather than expiry times
in its leases file. This also make dnsmasq "flash disk friendly".
Normally, dnsmasq tries very hard to keep the on-disk leases file
up-to-date: rewriting it after every renewal. When HAVE_BROKEN_RTC
is in effect, the lease file is only written when a new lease is
created, or an old one destroyed. (Because those are the only times
it changes.) This vastly reduces the number of file writes, and makes
it viable to keep the lease file on a flash filesystem.
NOTE: when enabling or disabling this, be sure to delete any old
leases file, otherwise dnsmasq may get very confused.
HAVE_TFTP
define this to get dnsmasq's built-in TFTP server.
HAVE_DHCP
define this to get dnsmasq's DHCPv4 server.
HAVE_DHCP6
define this to get dnsmasq's DHCPv6 server. (implies HAVE_DHCP).
HAVE_SCRIPT
define this to get the ability to call scripts on lease-change.
HAVE_LUASCRIPT
define this to get the ability to call Lua script on lease-change. (implies HAVE_SCRIPT)
HAVE_DBUS
define this if you want to link against libdbus, and have dnsmasq
support some methods to allow (re)configuration of the upstream DNS
servers via DBus.
HAVE_UBUS
define this if you want to link against libubus
HAVE_IDN
define this if you want international domain name 2003 support.
HAVE_LIBIDN2
define this if you want international domain name 2008 support.
HAVE_CONNTRACK
define this to include code which propagates conntrack marks from
incoming DNS queries to the corresponding upstream queries. This adds
a build-dependency on libnetfilter_conntrack, but the resulting binary will
still run happily on a kernel without conntrack support.
HAVE_IPSET
define this to include the ability to selectively add resolved ip addresses
to given ipsets.
HAVE_NFTSET
define this to include the ability to selectively add resolved ip addresses
to given nftables sets.
HAVE_AUTH
define this to include the facility to act as an authoritative DNS
server for one or more zones.
HAVE_DNSSEC
include DNSSEC validator.
HAVE_DUMPFILE
include code to dump packets to a libpcap-format file for debugging.
HAVE_LOOP
include functionality to probe for and remove DNS forwarding loops.
HAVE_INOTIFY
use the Linux and FreeBSD >= 15 inotify facility
to efficiently re-read configuration files.
NO_ID
Don't report *.bind CHAOS info to clients, forward such requests upstream instead.
NO_TFTP
NO_DHCP
NO_DHCP6
NO_SCRIPT
NO_LARGEFILE
NO_AUTH
NO_DUMPFILE
NO_LOOP
NO_INOTIFY
NO_IPSET
these are available to explicitly disable compile time options which would
otherwise be enabled automatically or which are enabled by default
in the distributed source tree. Building dnsmasq
with something like "make COPTS=-DNO_SCRIPT" will do the trick.
NO_GMP
Don't use and link against libgmp, Useful if nettle is built with --enable-mini-gmp.
LEASEFILE
CONFFILE
RESOLVFILE
the default locations of these files are determined below, but may be overridden
in a build command line using COPTS.
*/
/* Defining this builds a binary which handles time differently and works better on a system without a
stable RTC (it uses uptime, not epoch time) and writes the DHCP leases file less often to avoid flash wear.
*/
/* #define HAVE_BROKEN_RTC */
/* The default set of options to build. Built with these options, dnsmasq
has no library dependencies other than libc */
#define HAVE_DHCP
#define HAVE_DHCP6
#define HAVE_TFTP
#define HAVE_SCRIPT
#define HAVE_AUTH
#define HAVE_IPSET
#define HAVE_LOOP
#define HAVE_DUMPFILE
/* Build options which require external libraries.
Defining HAVE_<opt>_STATIC as _well_ as HAVE_<opt> will link the library statically.
You can use "make COPTS=-DHAVE_<opt>" instead of editing these.
*/
/* #define HAVE_LUASCRIPT */
/* #define HAVE_DBUS */
/* #define HAVE_IDN */
/* #define HAVE_LIBIDN2 */
/* #define HAVE_CONNTRACK */
/* #define HAVE_DNSSEC */
/* #define HAVE_NFTSET */
/* Default locations for important system files. */
#ifndef LEASEFILE
# if defined(__FreeBSD__) || defined (__OpenBSD__) || defined(__DragonFly__) || defined(__NetBSD__)
# define LEASEFILE "/var/db/dnsmasq.leases"
# elif defined(__sun__) || defined (__sun)
# define LEASEFILE "/var/cache/dnsmasq.leases"
# elif defined(__ANDROID__)
# define LEASEFILE "/data/misc/dhcp/dnsmasq.leases"
# else
# define LEASEFILE "/var/lib/misc/dnsmasq.leases"
# endif
#endif
#ifndef CONFFILE
# if defined(__FreeBSD__)
# define CONFFILE "/usr/local/etc/dnsmasq.conf"
# else
# define CONFFILE "/etc/dnsmasq.conf"
# endif
#endif
#ifndef RESOLVFILE
# if defined(__uClinux__)
# define RESOLVFILE "/etc/config/resolv.conf"
# else
# define RESOLVFILE "/etc/resolv.conf"
# endif
#endif
#ifndef RUNFILE
# if defined(__ANDROID__)
# define RUNFILE "/data/dnsmasq.pid"
# else
# define RUNFILE "/var/run/dnsmasq.pid"
# endif
#endif
/* platform dependent options: these are determined automatically below
HAVE_LINUX_NETWORK
HAVE_BSD_NETWORK
HAVE_SOLARIS_NETWORK
define exactly one of these to alter interaction with kernel networking.
HAVE_GETOPT_LONG
defined when GNU-style getopt_long available.
HAVE_SOCKADDR_SA_LEN
defined if struct sockaddr has sa_len field (*BSD)
*/
#if defined(__UCLIBC__)
#define HAVE_LINUX_NETWORK
#if defined(__UCLIBC_HAS_GNU_GETOPT__) || \
((__UCLIBC_MAJOR__==0) && (__UCLIBC_MINOR__==9) && (__UCLIBC_SUBLEVEL__<21))
# define HAVE_GETOPT_LONG
#endif
#undef HAVE_SOCKADDR_SA_LEN
#if defined(__UCLIBC_HAS_IPV6__)
# ifndef IPV6_V6ONLY
# define IPV6_V6ONLY 26
# endif
#endif
/* This is for glibc 2.x */
#elif defined(__linux__)
#define HAVE_LINUX_NETWORK
#define HAVE_GETOPT_LONG
#undef HAVE_SOCKADDR_SA_LEN
#elif defined(__FreeBSD__) || \
defined(__OpenBSD__) || \
defined(__DragonFly__) || \
defined(__FreeBSD_kernel__)
#define HAVE_BSD_NETWORK
/* Later versions of FreeBSD have getopt_long() */
#if defined(optional_argument) && defined(required_argument)
# define HAVE_GETOPT_LONG
#endif
#define HAVE_SOCKADDR_SA_LEN
#elif defined(__APPLE__)
#define HAVE_BSD_NETWORK
#define HAVE_GETOPT_LONG
#define HAVE_SOCKADDR_SA_LEN
#define NO_IPSET
/* Define before sys/socket.h is included so we get socklen_t */
#define _BSD_SOCKLEN_T_
/* Select the RFC_3542 version of the IPv6 socket API.
Define before netinet6/in6.h is included. */
#define __APPLE_USE_RFC_3542
/* Required for Mojave. */
#ifndef SOL_TCP
# define SOL_TCP IPPROTO_TCP
#endif
#elif defined(__NetBSD__)
#define HAVE_BSD_NETWORK
#define HAVE_GETOPT_LONG
#define HAVE_SOCKADDR_SA_LEN
#elif defined(__sun) || defined(__sun__)
#define HAVE_SOLARIS_NETWORK
#define HAVE_GETOPT_LONG
#undef HAVE_SOCKADDR_SA_LEN
#define ETHER_ADDR_LEN 6
#endif
/* rules to implement compile-time option dependencies and
the NO_XXX flags */
#ifdef NO_TFTP
#undef HAVE_TFTP
#endif
#ifdef NO_DHCP
#undef HAVE_DHCP
#undef HAVE_DHCP6
#endif
#if defined(NO_DHCP6)
#undef HAVE_DHCP6
#endif
/* DHCP6 needs DHCP too */
#ifdef HAVE_DHCP6
#define HAVE_DHCP
#endif
#if defined(NO_SCRIPT)
#undef HAVE_SCRIPT
#undef HAVE_LUASCRIPT
#endif
/* Must HAVE_SCRIPT to HAVE_LUASCRIPT */
#ifdef HAVE_LUASCRIPT
#define HAVE_SCRIPT
#endif
#ifdef NO_AUTH
#undef HAVE_AUTH
#endif
#if !defined(HAVE_LINUX_NETWORK)
#undef HAVE_NFTSET
#endif
#if defined(NO_IPSET)
#undef HAVE_IPSET
#endif
#if defined(HAVE_IPSET)
# if defined(HAVE_LINUX_NETWORK)
# define HAVE_LINUX_IPSET
# elif defined(HAVE_BSD_NETWORK)
# define HAVE_BSD_IPSET
# else
# undef HAVE_IPSET
# endif
#endif
#ifdef NO_LOOP
#undef HAVE_LOOP
#endif
#ifdef NO_DUMPFILE
#undef HAVE_DUMPFILE
#endif
#if !defined(NO_INOTIFY)
# if defined (HAVE_LINUX_NETWORK)
# define HAVE_INOTIFY
# elif defined (__FreeBSD__) && __FreeBSD__ + 0 >= 15
# include <osreldate.h>
# if __FreeBSD_version >= 1500068 /* 15.0.0 */
# define HAVE_INOTIFY
# endif
# endif
#endif
/* This never compiles code, it's only used by the makefile to fingerprint builds. */
#ifdef DNSMASQ_COMPILE_FLAGS
static char *compile_flags = DNSMASQ_COMPILE_FLAGS;
#endif
/* Define a string indicating which options are in use.
DNSMASQ_COMPILE_OPTS is only defined in dnsmasq.c */
#ifdef DNSMASQ_COMPILE_OPTS
static char *compile_opts =
"IPv6 "
#ifndef HAVE_GETOPT_LONG
"no-"
#endif
"GNU-getopt "
#ifdef HAVE_BROKEN_RTC
"no-RTC "
#endif
#ifndef HAVE_DBUS
"no-"
#endif
"DBus "
#ifndef HAVE_UBUS
"no-"
#endif
"UBus "
#ifndef LOCALEDIR
"no-"
#endif
"i18n "
#if defined(HAVE_LIBIDN2)
"IDN2 "
#else
#if !defined(HAVE_IDN)
"no-"
#endif
"IDN "
#endif
#ifndef HAVE_DHCP
"no-"
#endif
"DHCP "
#if defined(HAVE_DHCP)
# if !defined (HAVE_DHCP6)
"no-"
# endif
"DHCPv6 "
#endif
#if !defined(HAVE_SCRIPT)
"no-scripts "
#else
# if !defined(HAVE_LUASCRIPT)
"no-"
# endif
"Lua "
#endif
#ifndef HAVE_TFTP
"no-"
#endif
"TFTP "
#ifndef HAVE_CONNTRACK
"no-"
#endif
"conntrack "
#ifndef HAVE_IPSET
"no-"
#endif
"ipset "
#ifndef HAVE_NFTSET
"no-"
#endif
"nftset "
#ifndef HAVE_AUTH
"no-"
#endif
"auth "
#ifndef HAVE_DNSSEC
"no-"
#endif
"DNSSEC "
#ifdef NO_ID
"no-ID "
#endif
#ifndef HAVE_LOOP
"no-"
#endif
"loop-detect "
#ifndef HAVE_INOTIFY
"no-"
#endif
"inotify "
#ifndef HAVE_DUMPFILE
"no-"
#endif
"dumpfile";
#endif /* defined(DNSMASQ_COMPILE_OPTS) */
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